Method of sealing quartz to metal



Dec. 15, 1970 DAYTON ETAL 3,547,5D8

METHOD OF SEALING QUARTZ TO METAL Original Filed Nov. 25, 1966 2Sheets-Sheet 1 DAVID R. DAYTON PAUL E. GATES INVENTORS evxfiww mmTTORNEY L A T E.. M L O A T E Z T m N U. 00 WW I m. w D h 6 T9 1 5 2 0 Nd e l i F 1 a n i g 1 P 0 Dec. 15, 1970 2 Sheets-Sheet 2 DAVID R. DAYTONPAUL EGATES INVENTORS BY i I s ATTOR NFY United States Patent 3,547,508METHOD OF SEALING QUARTZ T0 METAL David R. Dayton, West Caldwell, N.J.,and Paul E. Gates, Danvers, Mass, assignors to Sylvania ElectricProducts Inc., a corporation of Delaware Original application Nov. 25,1966, Ser. No. 596,908. Divided and this application Apr. 1, 1969, Ser.No.

Int. Cl. HOlj 9/18 US. Cl. 31619 Claims ABSTRACT OF THE DISCLOSURE Thisapplication is a division of our copending application Ser. No. 596,908,filed Nov. 25, 1966, now abandoned.

This invention relates to lamps having tungsten filaments enclosed insealed envelopes, the latter being of fused quartz or other suitableglass. Such devices generally contain a halogen, such as iodine orbromine, and are usually called halogen quartz lamps. They operate on aregenerative cycle, initiated when a tungsten halide is produced andchemically combines with the particles evaporated from the incandescingtungsten filament. Subsequent thermal decomposition of this compoundreplaces the tungsten particles on the filament. More particularly, thisinvention concerns an improved method of sealing quartz lamps adapted tobe operational with high current loadings of the type described above.

Such high current lamps have many uses especially in the fields ofmotion pictures, television, photography and infrared heating. In theseindustries, an ever-increasing demand for more illumination has burdenedthe lamp manufacturer with added design problems. To appreciate theseproblems, it must be recognized that in the past, when the wattage of alamp was increased, the lamp envelope usually also increased in size. Inthe fields mentioned above, the demand for higher wattage lampsincreased to a point where thousands of watts were required. Thereforelamp envelope size became a burden to both lamp and fixture designers.

The lamp industry overcame this problem of increased lamp size by usingquartz envelopes and halogen fills so that wattage could be increasedwhile using smaller envelopes. However, with lamps of larger wattages amore perplexing problem was encountered in the fabrication of the seal.

Briefly, in the fabrication of quartz-halogen lamps of relatively lowwattage, the important sealing operation includes usin'g wafer-thinstrips of molybdenum as current conductors in the seal area. .Thesestrips were welded between a lead-in wire and a filament-support wire.This assembly was fitted into a quartz tubular envelope and afterheating of the quartz, a mechanical sealing die was brought intooperation. This sealing operation pinched the area where the molybdenumstrip bridged the lead-in wires and provided a vacuum-tight seal.Normally, on all standard low wattage lamps, this sealing operation wasadequate. But with the ever-increasing need for high watt- "ice age; themolybdenum foil strips could not wholly fulfill the need.

The problems encountered with the use of molybdenum foil as a sealconductor in high wattage lamps are many, but the most critical pointsare:

(A) The use of molybdenum foil in glass-to-metal seals requires the foilto be thin enough to be stretched by tensile stresses, but insufficientto break the glass seal, yet not so thin that the foil itself isfractured. Molybdenum strips as thin as 0.01 mm. are likely to befractured by tensile stress if the width exceeds 2 mm. Therefore a widerstrip would have to be made from thicker material, which in turn provedtoo heavy for trouble-free sealing from lamp-to-lamp.

(B) The production of this foil, such as molybdenum, by mechanicalmethods is also very difficult, so a more expensive method using an acidor electrolytic etching process is necessary to reduce the thickness ofthe foil to its final dimensions.

(C) Because of the small cross-section of the foil, the current-carryingcapacity is limited to about ten amps. Therefore, in fabrication of highcurrent lamps, it is necessary to try to utilize a multiplicity ofstrips for current-carrying.

(D) The fragile make-up of the foil made welding to other current leadwires a critical operation.

(E) Added problems were also encountered when current was passed througha multiple foil seal. Due to the low thermal conductivity of quartzglass, a continuous heat build-up in the foil caused a voltage dropacross the seal. For example, a voltage drop of as much as 1.5 volts ina 21W-l50W iodine-quartz lamp was noticed. Due to this change, a highervoltage was needed to give the required light output. Most filaments aredesigned to operate at their maximum electrical capacity and thereforeit was necessary to process them to withstand the added surges ofstarting voltages.

Accordingly, an object of our invention is to separate the seal from thecurrent-carrying path of the filament of the lamp.

Another object of our invention is to simplify the sealing of highwattage lamps.

A further object of our invention is to strengthen the lampconstruction.

An advantage of our invention is that it permits the use of extremelyhigh current through a quartz-to-metal seal, thus greatly extending therange of lamp sizes.

The various figures of the drawin'gs are the schematic view in thenature of a flow sheet depicting the various fabrication steps taken inour present invention.

In FIG. 1 a tapered conductor cup is shown in crosssection showing inparticular the taper and the centrally located hole.

FIG. 2 shows the tapered conductor cup completely sealed in glass.

FIG. 3 shows the encapsulated cup affixed to a glass tubular membershowing the outer glass removed midway of the tapered cup.

FIG. 4 shows two assemblies as described in FIG. 3 in position to beafiixed to a glass disc.

FIG. 5 shows the completed assembly of the tapered cups and glass disc.

FIG.6 shows a filament assembly positioned and welded to the taperedcup.

FIG. 7 shows a glass envelope sealed to the glass disc assembly withclamp legs fitted over the end wires and having an exhaust tubepositioned for final sealing of lamp.

FIG. 8 shows a complete lamp assembly.

In each of the figures of the drawing similar numerical designations areindicative of similar elements of structures.

In our present invention, we utilize a molybdenum cup as a sealingenclosure. In this way, the edges of the cup form a seal with a quartzenvelope. The base of the cup is provided with a centrally locatedaperture for the provision of a filament-supporting conducting rod thatis brazed or half-arc welded in place. This provides an unrestrictedcurrent-carrying path to the filament of the lamp. With this novelarrangement, the problems encountered with current-carrying conductorseals are eliminated.

Referring to FIG. 1 of the drawings, a tubular cup 10, made preferablyfrom molybdenum or similar metal, is shown in cross-section. The tubularcup 10 is constructed from material of about 0.010 in thickness,tapering from its base 12 to a feather edge 14 of about 0.002 inthickness. The central portion of the base of the cup is provided withan orifice 16. Cup 10 is the basic component of the seal portion of thelamp assembly. The feathered edge of the cup 10 will be sealed to thelamp and the orifice 16 will hold an electrical lead as will be furtherdescribed.

In FIG. 2 the first step in the assembly of the lamp is encapsulatingthe cup 10 with a jacket 18 of fused quartz or other suitable glass. Asviewed in FIG. 2 the cup is completely enclosed within a glass jacket 18having an appended exhaust tube 20 affixed thereto. A support portion ofthe exterior part of the jacket 18 is then cut from the cup 10. Thisleaves the lower half portion of the cup 10 exposed as viewed in FIG. 3.The inner wall of the cup 10 and the top part of the orifice 16 stillretain the glass jacket 18. Still referring to FIG. 3, a similardiameter tubular quartz sleeve 22 is then fused to the mouth of thejacket portion 18, thereby adding a section of glass approximately equalin length to that of the top glass jacket. With this operationcompleted, a finished subassembly 24 is realized. As viewed in FIG. 4,two similar subassemblies 24 can be seen prior to their attachment to aquartz disc 26 in a conventional glass fusing operation to provide abase assembly 23.

The quartz disc 26 as viewed in FIG. 4 is provided with a pair ofspaced-apart orifices. To fabricate the lam base 28 the end of thesleeves 22 are fitted into the orifices where a fusing operation joinsthe sleeve to the quartz disc 26.

A completed cross-section of the above described base assemblyarrangement 28 can be viewed in FIG. which shows the completeglass-covered interior wall. This assembly 28 is then ready to receive afilament structure 30, comprising a suitable coiled-coiled tungstenfilament 32. Filament 32 is supported equidistantly between a pair ofparallel tungsten rods 38 by a pair of short spuds 34 welded to the topof the tungsten rods 38 and penetrating several turns of the endportions of the coiledcoiled filament. The tungsten filament supportrods 38 are of different lengths as viewed in FIG. 6, one terminating atthe base of the filament and the other at its top. The rods 38 inconjunction with the short spuds 34 axially support the filament inrelation to the base assembly 28.

An ultrasonic drill is then utilized to clear the orifices of the glasscoating so that the filament assembly 30 can be fitted through theorifices 16 in the cups 10. The rods 4 38 are extended beyond the endsof the bases of the cups 10 to a desired length. A weld 40 is thenapplied to the rods 38 and the base 12 of cups 10 at the orifice 16.

As viewed in FIG. 6, the filament structure 30 is shown secured to thebase asembly 28. The filament structure 30 is then covered by a suitablequartz envelope 42 having an appended exhaust tube 44 aifixed thereto.The envelope 42 is heated in the vicinity of the disc 26 thereby fusingthe envelope 42 to the base assembly 28.

The lamp structure 46, as viewed in FIG. 7, is tipped at the exhausttube 44 after a series of exhausting and filling operations where apredetermined amount of halogen is added under the required conditions.

As viewed in FIG. 8, a completed lamp structure 46 is shown. After thefilling and tipping operation of the lamp envelope a final step isinitiated. A pair of metal end clamps 50 are fitted over each of themetal end cups 10 and rod ends 38. The clamps 50 are secured in place bysuitable set screws 52 that are tightened against the rod ends 38. Thisfinal step provides the lamp structure 46 with a uniform bi-prong baseto conform with the existing fixtures in industry.

While there has been shown and described what is at present consideredthe preferred embodiment of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims.

As our invention, we claim:

1. A process of sealing the ends of incandescent lamps having a tubularmetal cup at an end thereof and having a filament supported in acentrally located orifice in the base thereof the steps which comprise:encapsulating said cup in quartz glass; removing the lower exteriorportion of said glass to expose the base of said metal cup; fusing atubular quartz sleeve to the mouth of said cup; fusing said sleeve to aquartz disc; removing a portion of the quartz glass disposed near saidorifice; passing a rod adapted to support a filament through saidorifice into said cup; securing said rod to said cup at a point where itpasses through said orifice; placing a quartz envelope about said rod;fusing said envelope to said disc; exhausting said lamp envelope andfilling it with a suitable gas filling.

2. The process according to claim 1 wherein the width of the sides ofthe cup tapers to a feathered edge from the base.

3. The process according to claim 1 wherein there are two orificesdisposed in said quartz disc and each have a quartz envelope and cupdisposed thereon.

4. The process according to claim 1 wherein said cup and said rod areeach formed of a refractory metal.

5. The process according to claim 4 wherein said cup is formed ofmolybdenum and said rod is formed of tungsten.

References Cited UNITED STATES PATENTS H. A. KILBY, 111., PrimaryExaminer

